In ophthalmic surgery, and in particular in vitreo-retinal surgery, surgeons rely on a variety of techniques to provide contrast in order to visualize features of interest on the retina. Techniques that are commonly used are brightfield imaging, darkfield imaging, and gradient field imaging. Gradient field imaging is created by illuminating a feature by partially overlapping an illumination spot so that parts of the feature are well lit by direct illumination and parts of the feature are dim or back-lit by scattered light, or through dynamic contrast by moving an illumination beam over the retinal feature. Because endoscopic illumination is provided by inserting a probe tip through a small incision, the fact that the probe may have to be articulated through the incision point, and that the illumination probe is at a finite angel of incidence relative to a viewing microscope, providing desirable contrast is difficult to realize in a practical surgical setting.
Patterned (structured) illumination can be used to provide contrast by which a surgeon can visualize ocular structures, such as retinal structures. To obtain desirable contrast illumination, it is preferable to create a regular pattern of illumination (irregular illumination patterns, such as spiral ring patterns or donut patterns, do not provide favorable contrast). However, illuminator probes that can efficiently provide structured illumination safe for use in ophthalmic procedures are unknown.
FIGS. 1 and 2 illustrate a prior art method of illuminating an off-axis portion of the fundus with a pattern of linear stripes. Because the stripe pattern illuminates the fundus at an off-axis incident angle, any bumps or depressions in the retinal surface show as curved stripes to an observer (FIG. 3). When viewed through a fundus camera and analyzed, the stripes can be used to derive information about the retinal topography. However, this type of prior art illumination device requires a bulky, off-axis illumination system attached to the fundus camera by a bracket and is not useful for micro-surgery inside the eye.
Therefore, a need exists for an ophthalmic illuminator that can provide structured, safe illumination of a surgical field while overcoming the problems and disadvantages associated with prior art ophthalmic illuminators.